Denisovans, our newest old ancestor

We humans now have another confirmed cousin. Not quite Neanderthal, and not quite homo sapiens but clearly a separate lineage altogether.

As reported in a blog at Discover Online Magazine prior to being published in tomorrows New York Times, Carl Zimmer will be reporting on a paper in Nature which outlines the discovery of the linkage between Neanderthals, humans and the newest group of hominins given the name of Denisovans.

The link to Neanderthal man was found in mitochondrial DNA in a small finger bone and also a tooth. Both the tooth and finger bone were found in Denisova cave in Siberia.

Some of the more interesting aspects of the find were the linkages between the Denisovan DNA and the the people of New Guinea. As Zimmer notes, "you can't get there from here"

New Guineas is a very long distance from Siberia, but the new Guinean peoples genome carries as much as 4.8% Denisovan DNA.

The paper in question which was printed in Wednesday's Nature was written by an international team of scientists led by geneticist Svante Paabo, of the Max Planck Institute for Evolutionary Anthropology in Liepzig, Germany.

With the new data to use in modeling the spread of their ancestors from Africa it is proposed that the ancestors of Neanderthals and Denisovans left Africa roughly half a million years ago and spread themselves into two groups.

Neanderthals turned left, going west, while the Denisovans headed east where they probably interbred with humans moving out of Africa along the South Asian coast, and thereby leaving behind genetic markers found today in the New Guineans.

While Neanderthals lived in Europe, the Near East and Russia, from 240,000 to 30,000 years ago and left a sizable fossil record, it is suggested by Dr. Paabo and his fellow researchers that Neanderthals and humans had a common ancestor 600,000 years ago after analyzing the Neanderthal genome.

In the previous and separate study of the Neanderthal genome it was found by the scientists that the Neanderthal genome has more in common with the DNA of living Europeans and Asians than that of African DNA. That finding led the science team to study further afield.

A finger bone was sent to Dr Paabo from Anatoli Derevianko of the Russian Academy of Sciences with whom DR. Paabo's team had worked. The finger bone in question is that which was found in a the Denisova cave.

Harvard Medical School and the Broad Institute in Cambridge, Mass. researchers were chosen to conduct a study looking for comparisons to other species. The researchers including Nick Patterson, a Broad Institute geneticist compared the genome data with complete genome data for people from South Africa, Nigeria, China, France and Papua New Guinea. Patterson was very surprised.

“The correct reaction when you get a surprising result is, ‘What am I doing wrong?’ ” said Dr. Patterson.

After sequencing the finger bone genome and in the process Dr Paabo and his team while in Novosibirsk sharing the data with Derevianko, a tooth was offered by Dr. Derevianko for genome sequencing also. The tooth and the finger bone had nearly identical DNA.

The tooth proved to clearly be neither human or Neanderthal.

The focus now for Dr Paabo and his team is to find more fossils with the hope of finding a complete skeleton or at least a skull so they can get a glimpse of what the ancient Denisovans looked like.